Symptoms of halo blight start as small water-soaked spots on leaves, which gradually turn dark brown. The spots remain small and become surrounded by a wide yellow-green halo. The spread and development of halo blight is favored by wet weather and plant injury from rain, hail, people or equipment. Halo blight develops best when temperatures are somewhat cool, in the low to mid 70s. (Common bacterial blight and bacterial brown spot prefer warmer temperatures, in the 80°-90°F range.)
Plant disease-free seed, rotate crops, burn infected plant tissues and clean contaminated equipment. Avoid working with plants when they are wet, as bacteria are easily transmitted by water. To prevent infection, or reduce its spread, apply a copper soap fungicide at 7- to 10-day intervals. After heavy rain, or when disease is increasing rapidly, apply every 7 days, or more often, at the highest recommended rate. We recommend Soap-Shield Flowable Liquid Copper Fungicide.